Webcast Q&A: Motor Maintenance: The Predictive Way viewer questions answered

Vijay Anand, regional product specialist-condition monitoring & diagnostics for ABB was the presenter at the June 9 Plant Engineering Webcast, “Motor Maintenance: The Predictive Way.” An archive version of the Webcast is now available on the Plant Engineering Website.
By Plant Engineering June 15, 2015

Vijay Anand, regional product specialist-condition monitoring & diagnostics for ABB was the presenter at the June 9 Plant Engineering Webcast, “Motor Maintenance: The Predictive Way.”

Q: What should be used if the nameplate slip value may not be sufficient?
A: The actual operating slip will need to be calculated for each case. The name plate information is applicable for rated load conditions. While making measurements the load could be different which will cause the slip to change. Operating slip can be calculated by assessing the rotational speed of shaft the line frequency.

Q: What manufacture have meters to measure both electrical and vibration?
A: Of the current lot, I do not see any equipment manufacturer offering a kit that can make both electrical and mechanical measurements. The awareness of course is spreading fast and analysts see the value to have both vibration and electrical data (at least the current). ABB has custom-made equipment for the purpose but offers only service for making combined measurement.

Q: Can you clarify what size motors are considered medium and large motors? Can you classify by HP?
A: The classification is generally done in terms of voltage. In general, motors above 4KV are considered as medium voltage.

Q: What are the first steps to start a preventive plan? Is there a minimum size to start with and preventive maintenance sheet to use?
A: A complete survey of plant motors has to be carried out to determine critical, important, not-so-important motors. Critical are those which are critical for production/safety but may not have a standby. Important are those which are critical for production/safety but have a standby. The rest of the motors fall in the remaining group. Predictive maintenance could be started with Critical motors and extended to important motors.

Q: Inaccurate aligning of motor during installation could result in even a good motor to fail prematurely, leading to bearing failure of even affects the shaft. What are your comments on this?
A: Absolutely correct. Installation or mounting is one of the common reasons for premature failure of bearings. Improper mounting of bearing will induce pre-load resulting in higher stress on bearing than during normal condition.